**Core Concept**
The question is testing the student's knowledge of glucogenic amino acids, specifically the conversion of an amino acid to succinyl CoA, a key intermediate in the citric acid cycle. Succinyl CoA is a critical molecule in the metabolism of amino acids, serving as a precursor for the synthesis of glucose through gluconeogenesis.

**Why the Correct Answer is Right**
The correct glucogenic amino acid that forms succinyl CoA is **Threonine**. Threonine is converted to 2-Ketobutyrate via a transamination reaction. 2-Ketobutyrate is then converted to Acetohydroxy acid, which is further converted to Propionyl CoA. Propionyl CoA is then converted to Methylmalonyl CoA by the enzyme Propionyl CoA carboxylase. Methylmalonyl CoA is then isomerized to Succinyl CoA by the enzyme Methylmalonyl CoA isomerase. This conversion is a critical step in the metabolism of threonine, allowing it to be converted to glucose through gluconeogenesis.

**Why Each Wrong Option is Incorrect**
* **Option A:** This option is not a glucogenic amino acid, making it an incorrect choice.
* **Option B:** This option is not directly related to the formation of succinyl CoA, making it an incorrect choice.
* **Option D:** This option is not a glucogenic amino acid that forms succinyl CoA, making it an incorrect choice.

**Clinical Pearl / High-Yield Fact**
It's essential to remember that glucogenic amino acids can be converted to glucose through gluconeogenesis, making them critical for maintaining blood glucose levels. Threonine, in particular, is an essential amino acid that plays a crucial role in protein synthesis and metabolism.

**Correct Answer:** C. Threonine